How ATR FT-IR Can Help Determine Ages in Crime Victims

In a recent study led by Lenka Helamkova of Texas Tech University, researchers demonstrated the utility of attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectroscopy in determining ages of crime victims by sampling biological samples such as fingernails. The findings of the study were published in the Journal of Forensic Sciences (1). The results from this study serve as another reminder about the critical role spectroscopy plays in forensic investigations.

A victim’s age is an important variable that is considered during the criminal investigation and legal proceedings. The age of a victim is important for dictating the severity of the crime, and what the sentence should be for the convicted criminal. Forensic investigations are routinely used to help determine a deceased victim’s age during criminal investigations. Ultimately, forensic age estimations help courts and juries determine the age of someone whose actual age is unknown (2). In most cases, the victims could either be minors or illegal immigrants not documented in the system (2).

As a result, researchers have been exploring how spectroscopy and other analytical methods can be used to conduct age determination efforts in criminal investigations. Several spectroscopic techniques have been used to conduct analysis of biological fluids and samples to help identify victims. For example, ultraviolet-visible (UV-vis) and Raman spectroscopy have been used to analyze bloodstains to predict how long those stains have been there and to identify victims (3).

In this study, the researchers investigated whether ATR FT-IR spectroscopy can help estimate a victim’s age from nail samples, which are found associated with a crime scene or are occasionally left behind at a scene. As part of the experimental procedure, the research team gathered nail samples from donors across various age groups (1). Then, the researchers used ATR FT-IR spectroscopy and applied multivariate analysis to develop predictive models (1).

The researchers found that the partial least squares regression (PLS-R) model achieved promising accuracy in age estimation, with a root mean square error of prediction (RMSEP) of 11.1 during external validation (1). Furthermore, a partial least squares discriminant analysis (PLS-DA) model successfully classified donors into younger and older age groups with 88% accuracy during external validation (1).

However, the researchers cautioned that their study, while revealing the immense promise of ATR FT-IR spectroscopy in forensic age determination, does have limitations that future studies would need to investigate further. For example, the researchers discussed that their sample size for their experiment was limited (1). As a result, small variations between age groups could have been overlooked (1). The researchers also acknowledged that larger data sets will be needed to validate their findings (1). Because PLS-R and its performance is dictated by the size of the data set (regression models usually perform better with larger data sets), a larger data set will help confirm whether PLS-R is effective at recognizing patterns in the data (1).

However, despite these limitations, the researchers demonstrated the potential efficacy of ATR FT-IR in determining the ages of crime victims based on fingernail samples (1). The authors emphasized that their novel method is non-destructive, efficient, and practical, which can make it an optimal method to use for this type of work (1).

By leveraging chemical signatures in nails, the research provides a proof-of-concept for integrating advanced spectroscopic techniques into forensic investigations (1). The results indicate that ATR FT-IR spectroscopy, coupled with robust multivariate analysis, has potential to serve as a reliable method for age prediction, complementing existing forensic approaches and addressing the growing need for innovative analytical tools in criminal justice investigations.

References

1. Mitu, B.; Trojan, V.; Hrib, R.; Halamkova, L. Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) Analysis of Human Nails: Implications for Age Determination in Forensics. J. Foren. Sci. 2025, 70 (1), 150–160. DOI: 10.1111/1556-4029.15641
2. Schmeling, A.; Dettmeyer, R.; Rudolf, E.; et al. Forensic Age Estimation: Methods, Certainty, and the Law. Dtsch. Arztebl. Int. 2016, 113 (4), 44–50. DOI: 10.3238/arztebl.2016.0044
3. Gariglio, S.; Malegori, C.; Menzyk, A.; et al. Determination of Time Since Deposition of Bloodstains Through NIR and UV–Vis Spectroscopy – A Critical Comparison. Talanta 2024, 278, 126444. DOI: 10.1016/j.talanta.2024.126444